Sailing Theory

You don’t need to know much about how a piston engine works in order to drive a car. You get in, turn on the engine, shift into gear, step on the gas, and off you go.

In a sailboat, though, you play a far more active role in harnessing the energy that propels you forward. You can get stuck in “neutral,” with no wind in your sails – or you can even capsize – so it’s important to have a basic understanding of how a sailboat works.

It’s easy to see how a boat can sail when it’s going in the same direction as the wind; the sails catch the wind and push the boat forward. But how does a boat make progress sailing across the wind or even toward the wind? Why doesn’t a sailboat always get blown along with the wind?

Very simple, the forces of the wind on the sails (aerodynamics) and the water on the underwater parts of the boat (hydrodynamics) combine to propel the boat through the water. The wind blows across the sails, creating aerodynamic lift, like an airplane wing. The lift contains a sideways force and a small forward force. Trimming the sails efficiently produces the most forward force and the least resistance.

A sailboat would slide sideways with the wind if it did not have a centerboard or keel underneath the hull. The flow of water over the underwater surfaces creates lift, too – a sideways force countering the force of the wind. The combination of these forces pushes the boat forward.

Form stability and ballast keep a sailboat from tipping over sideways (capsizing). Keelboats have a heavy concentration of weight, usually lead, in their keels. As the boat heels, the weight of the keel pulls back down. Since centerboard boats don’t have heavy keels, the crew must use their weight to counteract the heeling forces. If you get too far out of position, you risk a capsize